Yidong Zhang

Design and growth of dendritic Cu2−xSe and bunchy CuSe hierarchical crystalline aggregations

Dendritic nanocrystals of copper selenide were fabricated in situ for the first time by using alcohol as the solvent. Cu2−xSe films composed of hierarchically ordered dendritic nanostructures were prepared on Cu substrates at a rather moderate temperature of 190–200 °C for just 1–3 h, while bunchy CuSe nanostructures could be further constructed above the Cu2−xSe dendrites by prolonging the reaction time of solvothermal growth with ethanol as the solvent. The resulting Cu2−xSe nanodendrites display highly symmetric corolitic morphology while the bunchy CuSe aggregations show particular nanostructures with a pronounced trunk and actinomorphic multi-branches. It is also found that the dendritic structures of crystalline Cu2−xSe could never be obtained when the reaction temperature is less than 190 °C, while the temperature needed is 160 °C for Ag2Se nanodendrites and higher than 220 °C for CdSe nanodendrites. These copper selenide nanostructures with hierarchically ordered 3-dimensional (3D) framework exhibited good absorbance and photoluminescence (PL) property and could bear potential applications in solar cell devices in the future.

From Nanoplates to Microtubes and Microrods: A Surfactant-Free Rolling Mechanism for Facile Fabrication and Morphology Evolution of Ag2S Films

By a simple and facile wet-chemistry technique without any surfactant, various shapes of Ag(2)S crystals--including leaflike pentagonal nanoplates, crinkly nanoscrolls, hexagonal prismlike microtubes, and microrods--were fabricated in situ on a large-area silver-foil surface separately. Detailed experiments revealed that the Ag(2)S nanoplates were formed just by immersing the silver foil in a sulfur/ethanol solution at room temperature and atmospheric pressure, and they subsequently rolled into nanoscrolls and further grew into microtubes and microrods under solvothermal conditions. Inspired by the natural curling of a piece of foliage, we proposed a surfactant-free rolling mechanism to interpret the observed morphological evolution from lamellar to tubular structures. Based on these simple, practical, and green chemical synthetic routes, we can easily synthesize lamellar, scrolled, tubular, and clubbed Ag(2)S crystals by simply adjusting the reaction temperature, pressure, and time. It is very interesting to note that the current rolling process is quite different from the previous reported rolling mechanism that highly depends on the surfactants; we revealed that the lamellar Ag(2)S could be rolled into tubular structures without using any surfactant or other chemical additives, just like the natural rolling process of a piece of foliage. Therefore, this morphology-controlled synthetic route of Ag(2)S crystals may provide new insight into the synthesis of metal sulfide semiconducting micro-/nanocrystals with desired morphologies for further industrial applications. The optical properties of the pentagonal Ag(2)S nanoplates/film were also investigated by UV/Vis and photoluminescence (PL) techniques, which showed large blue-shift of the corresponding UV/Vis and PL spectra.

Substitute of Expensive Pt with Improved Electrocatalytic Performance and Higher Resistance to CO Poisoning for Methanol Oxidation: the Case of Synergistic Pt-Co3O4 Nanocomposite

In this paper, Pt-Co3O4 nanocomposite was synthesized by a sol-gel process combined with electrodeposition method. Its electrocatalytic activity towards methanol oxidation was investigated at room temperature using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and current density-time curve. It is found that the resultant Pt-Co3O4 catalysts with minute amount of Pt exhibite attractive electrocatalytic activity for methanol oxidation reaction (MOR) but with a high resistance CO poisoning due to the synergistic effects from Pt and Co3O4. Together with the low manufacturing cost of Co3O4, the reported nanostructured Pt-Co3O4 catalyst is expected to be a promising electrode material for direct methanol fuel cells (DMFC).

Facile fabrication of CdS–poly(3-hexylthiophene) hybrid film with improved photo-current response for heterojunction solar cells

CdS nanostructured thin films have been directly fabricated on indium-tin oxide (ITO) glass substrates through a one-step solvothermal process involving a cadmium nanocrystal layer and sulfur powder in N,N-dimethyl formamide (DMF). Poly(3-hexylthiophene) (P3HT) was then infiltrated into the CdS framework. The CdS film and the CdS–P3HT hybrid film were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence spectroscopy (PL) and UV-vis spectroscopy. CdS–P3HT hybrid film exhibited a wider absorption in the solar spectrum and stronger photo-current response and external quantum efficiency than a pure CdS and P3HT film. Hybrid solar cell devices have been constructed based on the CdS–P3HT hybrid film with structure ITO–CdS–P3HT–Au. The effects of sulfur sources, solvent and thickness of elemental cadmium films on the photovoltaic performance of CdS–P3HT hybrid solar cells were assessed.

Tunable Morphology and Ethanol-Sensing Performance by Sintering Temperature of WO3-Based Ceramics

In this article, the authors describe how WO3 nanoparticles have been synthesized by sol-gel treatment from the precursor of W powder and H2O2 at room temperature, followed by sintering at 400°C, 600°C, 800°C, and 1000°C for 1 h, respectively. The samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Obtained results indicated that the gas-sensing properties to ethanol were decreased with the increasing sintering temperature from 400°C to 1000°C. The effects of sintering temperature on the gas-sensing characteristics of the WO3 ceramics were also investigated. The sensor that sintered at 400°C exhibited the maximum sensitivity to ethanol vapor at the operating temperature of 300°C. A possible mechanism for the influence of sintering temperature on the ethanol-sensing properties of WO3 sensors was proposed.

The First Observation of Ni and Ni2O3 Phases in the Sol-Gel Ag-Doped NiO Film

In this work, Ag-doped NiO film was prepared by a simple sol-gel method using the Ni (Ac)2. 4H2O and AgNO3 as precursor. The prepared films have been studied by X-ray diffraction (XRD), atomic force microscopy, X-ray photoelectron spectroscopy, and UV-visible spectrophotometer. Differently, some Ni or Ni3+ phases were found in the final films compared with previous reports. On the low concentration of Ag doping (1.5 mol%), the Ag-doped NiO film had formed the solid solution. The obvious phase separation was observed when the concentration of Ag dopant reached to 10% (mol).

An Au buffer layer for the growth of a ZnO sol–gel film on a Si substrate

In this work, we demonstrate the influence of an Au buffer layer on the structure and photoluminescence (PL) properties of ZnO sol–gel thin films on Si substrates. An Au layer was deposited on the silicon substrate by the evaporation deposition method from highly pure Au (99.99%) wires. Then, a ZnO film was prepared by the sol–gel method with spin-coating technology, followed by calcinations in air at 600 °C for 1 h. The structures and morphologies of the prepared films were characterized by x-ray diffraction, energy dispersive spectrum analysis, atomic force microscopy and PL. The results show that the prepared ZnO thin film with an Au buffer layer exhibits good crystallinity and surface morphology compared with that without an Au buffer layer. Interestingly, different from other previous reports on buffer layers with PL-enhanced properties, the ZnO thin film with Au buffer layer showed an obvious violet PL-quenched property.